Because of their structural efficiency, certain forms of structures are preferred for use in space where considerations of size, weight and transportability are important. Among these are truss structures, which have a high stiffness-to-weight ratio and a simple, self-determined geometry. Since structures of substantial size are not transportable into space but must be erected on site, it is a primary requirement that the method and apparatus employed be as simple as possible and that it preferably enable construction and disassembly from a single general location. Further, the stowage efficiency of the structure must be high for purposes of transport.
It is also desirable that the construction be automated to the greatest extent possible in order to minimize the requirement for human participation. Further, considerations of weight and efficiency dictate that the equipment for carrying out such automated construction in space be light and relatively small, or be capable of being transported in disassembled condition. Also, for purposes of repairing the truss structure, or in applications where the use of the truss structure is temporary, it is desirable that the construction apparatus also be capable of disassembling the built-up truss structure.
Structures currently in use, or proposed for use, in space are subject to a number of disadvantages. Self-deployable structures which automatically unfold and position themselves in space are generally not efficient and frequently carry a weight penalty because of the self-deployment feature. Also, structures which are capable of automated construction in space often fail to achieve the necessary stiffness-to-weight ratio, stowage efficiency and the requisite simplicity of the assembly method and apparatus. Further, existing structures for use in space typically fail to provide assembly from a single general location.
By way of example, U.S. Pat. No. 4,337,560 to Slysh discloses a structure that lends itself to an automated assembly technique, but is subject to several disadvantages. In particular, the structure disclosed in the Slysh patent is incapable of construction from one fixed, general location. To overcome this deficiency, Slysh provides an assembler trolley which must crawl along the erected structure, somewhat analogous to the elevators employed in the construction of a high rise building, as the structure is built up during construction. Such apparatus not only adds to the weight that must be transported into space, but it materially increases the complexity of constructing a structure in space.